The present invention relates to the enforcement of speed limits on vehicles traveling on roadways.
With a constant increase in the number of vehicles, the number of accidents has increased dramatically. Speeding is widely recognized as the number one cause of road accidents and fatalities every year. An article published by the U.S. Department of Transportation's Federal Highway Administration named “Synthesis of Safety Research Related to Speed and Speed Limits” provides a summary of speeding-related road accidents. The summary states:                That the evidence shows that the risk of having a crash is increased for vehicles traveling above the average speed.        That the risk of being injured increases exponentially with speeds much faster than the median speed.        That the severity of a crash depends on the vehicle speed change at impact.        
Problems in traffic speed control and traffic violations have been studied extensively over the last few decades. A number of devices have been introduced to improve the detection and prosecution of traffic violations. The use of radar devices to detect and record vehicle speed began in the 1950s. From a stationary base station, radar waves are emitted and are backscattered by a mobile object. Video cameras were introduced a little later to capture sequential images to document traffic speed violations.
Currently, most conventional attempts for real-time traffic speed control and detection use a wheel-speed measuring device, are Doppler-radar based, laser based or use road sensors of some kind. Unfortunately, those means are not always accurate and sometimes require a human operator. Radar-based and laser-based systems are known in particular for their inaccuracy.
As an example of vehicle speed being measured by calculating detection values from wheel speed sensors, Seto in his U.S. Pat. No. 6,339,740 disclosed a machine for detecting vehicle traffic offenses. This machine comprises a speed-detection means for measuring the speed of transit of a vehicle along a carriageway by detecting the interception of a beam or field by the front or rear of the vehicle, said speed detection means being arranged on a side of the carriageway and camera means for capturing an image of the vehicle, said camera means being connected to said speed detection means and to said carriageway transverse position detection means, said camera means being controlled as a function of said traverse position.
For another example, Adachi in his U.S. Pat. No. 6,975,931 describes a system for measuring speed according to regular speed measuring methods available in all the vehicles today, receiving that data and for setting maximal speed limits according to speed limits used in different countries.
For yet another example, Yoshino in his European Patent EP0476582 discloses an apparatus for detecting motorcycles' speed based on a front wheel speed and a rear wheel speed, and applying antilock brake control to each of front and rear wheels based on a calculated estimated vehicle speed. The apparatus includes a memory for storing the estimated vehicle speed at the time an application of antilock brake control to either the front or rear wheel is started, or an application of brakes to either the front or rear wheel starts. The apparatus further includes a calculation unit for comparing the front wheel speed and the rear wheel speed to calculate the estimated vehicle speed based on the higher of the front wheel speed or the rear wheel speed, while antilock brake control is applied to the front or rear wheel or either a front brake or a rear brake is applied.
Sensor-based vehicle speed detection systems provide another part of the prior art. An example of such a system can be viewed in the paper named “Vehicle Speed, Direction, ID Sensing for PRT” by G. B. Lee, J. H. Heo, and J. S. Lee (Korea). This paper presents the vehicle speed, direction, identification sensing methods for vehicle speed determination. The speed of the vehicles is measured using different proximity sensors, wherein two proximity sensors are utilized to detect the direction of the vehicle and to measure the speed of the vehicle.
Camera-based vehicle speed-detection systems constitute yet another part of the prior art. An example of such a system can be viewed in the paper named: “Vehicle Speed Detection and Identification from a Single Motion Blurred Image.” Proceedings of the Seventh IEEE Workshops on Application of Computer Vision (WACV/MOTION'05)—Volume 1, 5-7 Jan. 2005. Pages: 461-467.
The paper discloses a system in which motion blur is a result of finite acquisition time of practical cameras and the relative motion between the camera and moving objects. The paper presents an improvement over RADAR-based devices. In the paper, Lin produces a novel approach in which the motion blur parameters are estimated from a single motion blurred image and the length of motion blur is used for image restoration. The restored image is then used to obtain other parameters for vehicle speed estimation. The images taken with the vehicle's license plates are used for both the assistance of image restoration and the identification of the vehicle. The author reports to have established a link between the motion-blur information of a 2D image and the speed information of a moving object. The paper further states that experiments have shown the results of less than 2% error for both local and highway traffic compared to video-based speed estimation methods.
RADAR-based vehicle speed detection systems constitute yet another part of the prior art. Chubbs, in his U.S. Pat. No. 6,400,304, presents a system that combines a global positioning satellite (GPS) system and a radar detection unit, in wireless communication with the GPU, for tracking and determining the speed of a vehicle. The system may be manually activated, or more preferably, activated by an external source of radar signals, such as may be emitted by a police “speed trap.” The unit includes means for recording and storing speed data of the vehicle, and to alerting the operator of the vehicle to a “speed trap” situation.
Another example of using a GPS device to determine speed of the vehicle is shown by Flanner in U.S. Patent Application Publication 2007/0271020 for “Motor vehicle speed detection and control system.” Flanner discloses a GPS-based system disposed within a motor vehicle configured to measure the geographic coordinates of the vehicle in order to calculate and adjust and maintain the current speed of the vehicle to correspond to the speed limit of the determined geographic coordinate. The system further includes a database that contains roadmaps and corresponding speed limit data. A coordinate-determination system calculates the current geographic coordinate of the vehicle to calculate the current speed data of the vehicle and subsequently performs an algorithm to compare the current-speed data with the speed-limit data stored in the database for the current geographic coordinate.
U.S. Pat. Nos. 6,466,862 and 6,785,606 disclose a combination of video cameras, road-mounted pressure sensors, GPS receivers, and cell phone signal triangulation to determine the locations and speeds of vehicles moving along roads. These patents disclose systems for providing traffic flow information to vehicle operators and do not contemplate law enforcement applications such as determining whether vehicles are moving faster than corresponding speed limits or issuing tickets for traffic violations.
A couple of patents disclose determining the distance between a cellular base station and a moving object. Neither provides speed estimates nor deals with traffic violation based on those estimates. For one, U.S. Pat. No. 7,205,931 discloses a method for determining the distance between a base station (SLG) and a mobile object (DT1-DT3). The reference also discloses a base station and identification system for a method of this type. As disclosed in the abstract of the reference, A HF carrier frequency and an offset frequency (df) are predetermined for a QAM modulation. The HF carrier frequency is increased and decreased by the offset frequency in sequence over time in such a way that the HF carrier base frequencies (fo+df, fo−df) result in an HF carrier signal (TS) thus modulated to exhibit an identical phase when the frequency is changed. The HF carrier signal is subsequently transmitted and simultaneously mixed (MIX) with an HF carrier signal (RS) that has been backscattered by the mobile object to obtain a carrier phase signal (PS). The corresponding carrier phase (PH1, PH2) for the two HF carrier base frequencies is determined in sequence over time. The difference (dPH) between these phases is used to calculate the distance between the base station and the respective mobile object.
U.S. Pat. No. 7,269,387, named: “Method and apparatus for determining a distance between a base station and a mobile unit,” provides a method and an apparatus for determining a first estimate of a distance traveled by a signal on a wireless communication link between the base station and the mobile unit, determining a second estimate of the distance traveled by the signal on the wireless communication link between the base station and the mobile unit, and comparing the first and second estimates.
Additionally, the company TruePosition, Inc. offers products for tracking the locations of cellular phones based only on their wireless signal, without aid from GPS. One product, the TruePosition Location Platform is widely used in the United States by AT&T and T-Mobile to meet the FCC's E-911 requirements of detecting the location of a cell phone for dispatch of emergency services. The TruePosition Location Platform uses Uplink Time Difference of Arrival techniques, disclosed in U.S. Pat. No. 5,327,144 which is incorporated herein by reference, as a source for obtaining the location of a cell phone based on a normal cellular signal. The Platform can be supplemented with location data obtained through Angle of Arrival techniques, which are discussed later in this specification. Another product, TruePosition LOCINT, collects, stores, analyzes, and displays historical and real-time wireless events and location of targeted cell phone users.
Over the years, devices have been introduced to improve the detection, documentation, and prosecution of traffic violations. Recently, a number of unmanned-camera-based and radar-based systems for detection and documentation of speeding have been installed. These systems produce visual images of the speeding offense, those images to be processed later by police personnel, producing speeding tickets, which are mailed to the registered owner of the vehicle. However, all the devices and processes still require police personnel attention to process each traffic violation. Police personnel efforts are not only time-consuming but also expensive.